Process of producing thermoplastic starch/polymer blends

Abstract

A process of producing a thermoplastic starch/polymer blend involves introducing dry starch into a twin-screw extruder at a first location along the extruder, introducing a plasticizer into the twin-screw extruder at a second location along the extruder downstream of the first location to form a starch paste and then gelatinizing the starch paste in the extruder to form thermoplastic starch, and, introducing dry polymer at ambient temperature into the twin-screw extruder at a third location along the extruder downstream of the second location to form a blend with the thermoplastic starch in the extruder.

What is claimed is: 
     
       1. A continuous process of producing a thermoplastic starch/polymer blend comprising:
 (a) introducing starch in a dry form into a twin-screw extruder at a first location along the twin-screw extruder; 
 (b) introducing a plasticizer into the twin-screw extruder at a second location along the twin-screw extruder downstream of the first location to form a starch paste and then gelatinizing the starch paste in the twin-screw extruder to form thermoplastic starch; and 
 (c) introducing dry solid polymer at ambient temperature into the twin-screw extruder at a third location along the twin-screw extruder downstream of the second location to form the thermoplastic starch/polymer blend with the thermoplastic starch in the extruder, 
 wherein the formation of thermoplastic starch in step (b) and the formation of the thermoplastic starch/polymer in step (c) occurs sequentially and in the same twin-screw extruder. 
 
     
     
       2. The process according to  claim 1 , wherein the plasticizer comprises a polyfunctional alcohol. 
     
     
       3. The process according to  claim 1 , wherein the plasticizer comprises water and a polyfunctional alcohol in a ratio in a range of from 0.01:10 to 5:10 w/w water:polyfunctional alcohol. 
     
     
       4. The process according to  claim 3 , wherein the ratio of water:polyfunctional alcohol is in a range of from 0.5:10 to 2:10 w/w. 
     
     
       5. The process according to  claim 2 , wherein the polyfunctional alcohol comprises glycerol, sorbitol or a mixture thereof. 
     
     
       6. The process according to  claim 2 , wherein the polyfunctional alcohol comprises sorbitol. 
     
     
       7. The process according to  claim 1 , further comprising removing water from the thermoplastic starch before introducing the dry solid polymer. 
     
     
       8. The process according to  claim 1 , further comprising extruding the thermoplastic starch/polymer blend through an extrusion die to directly form a final product or into an extrudate that will be pelletized prior to further processing. 
     
     
       9. The process according to  claim 1 , wherein the dry solid polymer is in solid pellet or powder form. 
     
     
       10. The process according to  claim 1 , wherein the dry solid polymer comprises polyethylene, polypropylene, polystyrene, poly(lactic acid), poly(s-caprolactone), polybutylene succinate, copolymers thereof or mixtures thereof. 
     
     
       11. The process according  claim 1 , wherein the dry solid polymer is compatibilized with the thermoplastic starch with a compatibilizer. 
     
     
       12. The process according to  claim 11 , wherein the compatibilizer comprises an unsaturated carboxylic acid anhydride. 
     
     
       13. The process according to  claim 1 , wherein the plasticizer is introduced in an amount of 40 wt % or less based on a weight of the starch in a dry form.